Aluminum chlorhydrates (also referred to as aluminum chlorhydroxides or basic aluminum chlorides) have been known and used for many years as effective antiperspirants, and still constitute the essential active ingredient in many antiperspirants today. The aluminum chlorhydroxides are complex structures made up of mixtures of polymeric and monomeric species of various sizes and molecular structures, together with varying amounts of bound or coordinated water. They are generally represented by the empirical formula: EQU Al.sub.2 (OH).sub.(6-x) Cl.sub.x
wherein O&lt;x&lt;6 and need not be an integer. It should be understood that the above formula is greatly simplified and is intended to include basic aluminum chlorides containing coordinated or bound molecules of water as well as basic aluminum chloride polymers, complexes and mixtures of the above.
Particularly preferred aluminum chlorhydrates are those in which x is in the range of about 1 to 2, and preferably about 1, the latter being referred to as five-sixths basic aluminum chloride. Such compounds have a predominance of units of the above formula in which x is between about 1 and 2, such that the aluminum to chlorine mole (Al/Cl) ratio is on the order of about 1/1 to 2.1/1, and usually in the range of about 1.9/1 to 2.1/1.
For many years five-sixths basic aluminum chloride has been recognized as the standard active ingredient for antiperspirants. It has been available in various forms, typically in 50 weight percent aqueous solution (commercially available from Reheis Chemical Company under the trademark "CHLORHYDROL"), but also in various dry forms obtained by spray drying aqueous solutions to an extent which does not remove all of the bound or coordinated water. In addition, these compounds may be co-dried or otherwise combined with any of a number of adjuvants and/or additives designed to perform various functions, such as buffers; these could include such moieties as glycine, urea, polyols, etc.
In the past twenty years many attempts have been made to improve the antiperspirant efficacy and other properties of the basic aluminum chlorides, some by the formation of complexes with various organic and inorganic additives to the basic aluminum chloride complexes. Among the attempts to modify the complex structure of the basic aluminum chlorides without the addition of other entities, three are noteworthy in relation to the present invention.
U.S. Pat. No. 3,904,741 of Jones et al (assigned to the same assignee as the present invention) discloses two-thirds to five-sixths basic aluminum chloride solids which have been rendered alcohol soluble by heating a solution of basic aluminum chloride under reflux conditions, preferably to a temperature of about 100 degrees C. for about two to four hours, and then drying the refluxed solution, preferably by spray drying, to a carefully controlled content of free and coordinated water. The patentees theorized that the refluxing promoted a shift in the species of basic aluminum chloride molecules from higher molecular weight to lower molecular weight species.
More recently, published British patent application No. 2,048,229 of Fitzgerald et al (assigned to the Gillette Company) disclosed a modification of aluminum chlorhydroxide, preferably five-sixths basic aluminum chlorhydroxide, by aging a 5 to 40 weight percent solution (most preferably a 10 to 25 weight percent solution) at a temperature between 50 and 100 degrees C. for a period of at least eight hours up to a week or more. The type of aging vessel is not stated, but it is apparently an open, non-pressurized vessel with compensation being made for loss of water during heating; otherwise a dried solid could result. After aging the solution can be concentrated by distillation and then spray dried. According to this patent application the aging process modifies the aluminum chlorhydroxide by increasing the amount of the more efficacious group of Al.sup.c' complexes (as defined in the British application) from about 10 to 30 weight percent in conventional aluminum chlorhydroxides to a level of at least 45 weight percent and preferably more than 60 or 70 weight percent in the aged aluminum chlorhydroxides. These higher percentages of Al.sup.c' complexes are broadly characterized by their diffusion constants in gel permeation chromatography.
Another recent modification of basic aluminum compounds is disclosed in U.S. Pat. No. 4,359,456 of Gosling et al (assigned to Lever Brothers Company). According to the method of that patent, a wide range of basic aluminum chlorides in a 10 to 34 weight percent aqueous solution (2.5-8.5 weight percent aluminum) is heated to a temperature of 50 to 140 degrees C. for a period of time sufficient to cause the basic aluminum compound to have a Size Exclusion Chromatography Test Band having a relative retention time corresponding to Band III of the standard basic aluminum chloride solution Size Exclusion Chromatogram and a Band III Aluminum Value of at least 20 percent. The heating is carried out for a period of from one-half hour to 30 days in a closed tube, bottle or reactor, followed by cooling to ambient temperature and drying to a water soluble powder. The increase of the percentage of aluminum in the Band III fraction to a level of 20 percent or more is said to result in an enhancement of the antiperspirant activity of the basic aluminum chloride. In contrast, according to that patent, 40 or 50 weight percent solutions of approximately five-sixths basic aluminum chloride heated to 120 degrees C. for 24 hours in glass screw-cap tubes did not result in enhanced antiperspirant activity or Band III levels of aluminum greater than 20 percent by weight.